Malware authors have ported
a Trojan originally written for Linux systems to hijack Mac OS X systems,
security researchers found. Once compromised, the Macs could be used to launch
denial-of-service attacks.
The Tsunami Trojan works by
latching onto a host. Tsunami appears to be derived from Kaiten, an old
backdoor Trojan, dating back at least to 2002, that was designed to infect
Linux systems, Robert Lipovsky, a malware researcher at ESET wrote in an Oct.
25 blog. The Trojan is also evolving pretty quickly, as ESET researchers
discovered at least one new variant by Oct. 27, according to Pierre-Marc
Bureau, a senior malware researcher at ESET.

The Trojan is named for its
likely goal, to force infected computers into becoming part of a compromised
network to launch distributed-denial-of-service (DDoS) attacks, flooding
Websites with traffic and causing them to stop responding, according to Graham
Cluley, a senior technology consultant at Sophos.

"Even though there is
far less malware in existence for Mac OS X than for Windows, that doesn't mean
the problem is nonexistent," Cluley wrote on the Naked Security blog.
Once the Trojan program has
been copied onto the system, either intentionally or maliciously, the malware
attempts to connect to an Internet Relay Chat channel to receive further
instructions. The malware can launch DDoS attacks at a targeted server,
download additional malware on the machine and provide remote access to the
system, Cluley said.
The new variant has the
ability to make itself launch automatically on reboot, causing it to be more
persistent on the system, Bureau said. It also had an updated command and
control IRC server and channel than what was included in the previous version.

There are "very few
hosts" infected with this malware, Bureau said, noting that the developers
are most likely still in the process of testing the application.
The Kaiten source code has
been publicly available since at least September 2009, and it was
"trivial" to compile the code, using Apple's XCode, to create a Mac-executable,
Mac security company, Intego noted on its blog. Intego also noted that people
may intentionally install the Trojan on their systems if they voluntarily take
part in DDoS attacks, such as those supporting Anonymous operations.
Those "volunteers"
have "effectively put control" of their Macs into someone else's
hands, Cluley said.
While there have been many
instances of Windows malware re-engineered for the Mac platform, Tsunami
appears to be the first that takes advantage of the fact that Mac OS X is based
on BSD, an operating system with many similarities with Linux.
"If the bad guys think
they can make money out of infecting and compromising Macs, they will keep
trying," Cluley said, predicting more malware targeting "poorly
defended Mac computers."
There has been a flurry of
Mac malware activity recently. Beginning in September, F-Secure researchers
found the Revir/Imuler Trojan, which was spread through malicious PDF files.
Another Trojan-called Flashback because it masquerades itself as an update to
Adobe Flash, or Flash Player installer-was detected in late September and went
through various iterations this month, according to F-Secure. New capabilities
include the ability to detect if the Mac had a firewall installed as well as the
ability to search for virtual machines. If these were found, the malware
deleted itself.
The latest Flashback was far
more sinister, as it could disable Apple's built-in Xprotect malware detection
system by overwriting certain Xprotect files to prevent the system from getting
new signature updates. Intego said Flashback was the first Mac malware that
could "intentionally" damage system files. Removing the malware and
restoring the system could be time-consuming, Intego noted.
"We hope Mac malware
doesn't use similar techniques in the future that would require a full
installation of Mac OS X to repair damage," Intego said.
Cluley warned Mac users to
protect themselves from cyber-threats with proper security software.
"Don't be a soft target; protect yourself," he said.